Amorphous silicon films can used in a variety of semiconductor manufacturing applications. For example, amorphous silicon is often used, as a sacrificial layer in a self-aligned double patterning (SADP) process or a self-aligned quadruple patterning process (SAQP). Amorphous silicon material is typically deposited on a semiconductor wafer disposed atop a substrate support located within a process chamber. A process such as physical vapor deposition (PVD) may be used to deposit the material. During deposition, however, the amorphous silicon is not only deposited on the semiconductor wafer but is also deposited on inner surfaces of the process chamber, such as on a shield, a deposition ring, a cover ring, and/or chamber walls of the process chamber. The deposited amorphous silicon material may form a high-stress film on the semiconductor wafer and on the inner surfaces of the process chamber.
In addition, when a process is carried out in the PVD process chamber, the inner surface of the process chamber typically goes through a thermal cycle, expanding as the inner surface heats up at the beginning of the cycle and contracting as the inner surface cools down at the end of the cycle. The thermal cycle is repeated in the process chamber each time that a process is carried out. The inventors have observed that the high stress on the film deposited on the inner surface of the process chamber, in combination with the repeated thermal cycling of the process chamber, undesirably causes the film to delaminate and generate particles. Typically, smaller particles are generated during thermal expansion, and larger particles are generated during thermal contraction, which is known as flaking.
The problem of flaking and particle generation could be addressed by performing preventive maintenance on the process chamber, such as by replacing the shield or other components within the process chamber. However, as device geometries have shrunk, and particle size and particle limit specifications have therefore tightened, the frequency of such preventive maintenance would also increase, undesirably resulting in increased downtime and higher cost of operating the process chamber.
Accordingly, the inventors have provided improved methods and apparatus for reducing the number of particles generated during a process carried out in a process chamber.